The present invention relates to an aerosol guiding device and an aerosol generating system containing said aerosol guiding device. More particularly, it relates to an aerosol guiding device for controlling and modifying air flow for use in an aerosol generating system such as an electronic cigarette.
Aerosol generating systems such as electronic cigarettes are becoming well known in the art. The operating principle for these electronic cigarettes usually centres around providing a flavoured vapour to a user without burning material. Some known devices comprise a capillary wick and a coil heater, which can be activated by the user through suction on a mouthpiece of the device, or by for example activating a push button on the device. This switches on a battery power supply that activates the heater, which vaporises a liquid or solid material. Suction on the mouthpiece further causes air to be drawn into the device through one or more air inlets and towards the mouthpiece via the capillary wick, and the vapour that is produced near the capillary wick mixes with air from the air inlet and is conveyed towards the mouthpiece as an aerosol.
An important factor in the design of aerosol generating systems such as electronic cigarettes is the regulation of air flow within the system, which impacts upon the quality and quantity of aerosol delivered to the user. Particle size of the aerosol is also an important consideration, and optimum particle size of the aerosol may be determined for optimum delivery of said aerosol to the lungs; aerosol particles that have diameter greater than for example 1.0 micrometre may be trapped or obstructed before they reach the lungs, and aerosol particles having diameter for example smaller than 1.0 micrometre may be delivered more effectively to the lungs.
Some attempts have been made to address the above problems. For example, with the device of EP2319334A1, air flow speed may be controlled within the device by varying the cross sectional area of the air flow route upstream of the capillary wick so as to take advantage of the Venturi effect. Air flow through a constricted section increases in speed in order to satisfy the principle of continuity, while its pressure must decrease in order to conserve mechanical energy. Similarly, air flow through a wider section must conversely decrease in speed, whilst its pressure increases.
A problem with known devices that attempt to control air flow speed, however, is that inconsistencies within the system, for example due to manufacturing tolerances, or inconsistencies due to external factors, for example varied suction of a user, may lead to a consequent variance in the resultant air flow within the aerosol generating system. For example, the pressure drop in vaporisation chambers of current models of electronic cigarettes sometimes varies widely between 40 mmWC and 250 mmWC, and more commonly between 100 mmWC and 125 mmWC. In addition, there are often significant inconsistencies in the pressure drop achieved in vaporisation chambers used across electronic cigarettes of the same model. A further problem is that if these inconsistences arise in a particular design of electronic cigarette, it is almost impossible to then change that design in order to further modify air flow, thus resulting in lack a flexibility of the entire system.
Due to the inconsistency in pressure drop within current aerosol generating systems, it is possible that no liquid or solid material to be vaporised may be present on the wick when a user provides suction action on the mouthpiece. This leads to an unpleasant effect called “dry puffing” where the capillary wick is burnt by the heater and a burnt taste is experienced by the user. In other cases, too much liquid or solid material may be present on the capillary wick, in which case the heater cannot vaporise all of said material, thus resulting in an inefficient system.